The present invention relates to an apparatus and a method for displaying a three-dimensional image based on a plurality of Doppler image data and an ultrasonic diagnosis apparatus using the same.
An ultrasonic diagnosis apparatus for obtaining Doppler data and displaying a two-dimensional color Doppler image based on the Doppler image data has been heretofore offered. ("Real Time Two-Dimensional Doppler Echocardiography" pp. 6-13, edited and written by Ryozo Omoto, published on Dec. 9, 1983 by Diagnosis and Remedy Co., Ltd.)
First, the color Doppler image mentioned above will be described.
The color Doppler image is an image obtained by generating ultrasonic beams 2 from a probe toward a blood vessel 1 at a diagnosis region in an object to be examined as shown in FIG. 7A, receiving a reflected echo from the blood vessel 1 so as to detect a Doppler signal, and displaying an image after appropriate coloration in accordance with information contained in the Doppler signal.
In the color Doppler image, a flow such as a blood flow moving on toward the ultrasonic beam generated by the probe is displayed in a warm color (R+G) obtained by mixing a red color (R) and a green color (G) with each other in an appropriate ratio, and a flow getting away from the ultrasonic beam generated by the probe is displayed in a cold color (B+G) obtained by mixing a blue color (B) and a green color (G) with each other in an appropriate ratio, and the faster flow is shown as the display gets brighter. Further, the green color (G) is controlled by the variance of the blood flow velocity, and display is made by increasing the green color (G) as the variance gets larger.
With this, a blood flow having large variance which moves on toward the ultrasonic beam generated by the probe is displayed in a yellow color, the blood flow having small velocity variance is displayed in a red color, and further, a blood flow having large velocity variance getting away from the ultrasonic beam generated by the probe is displayed in a bluish green color, and the blood flow having small velocity variance is displayed in a blue color.
The Doppler image data are composed of three data, i.e., data 5 for a red color (R), data 6 for a green color (G) and data 7 for a blue color (B) as shown in FIG. 8 for expressing the velocity information and the velocity variance information taking a case that the ultrasonic beams 2 are generated as shown in FIG. 7A on a blood flow shown with an arrow mark 3 containing a turbulent flow 4 therein as shown in FIG. 7 (b) as an example. Further, as shown in FIG. 8, a color Doppler image 8 is displayed by superposing these data after applying D/A conversion, respectively.
Further, in order to display a fast flow bright, the data for red color (R) and data for blue color (B) show higher brightness in respective colors as the value of the data gets bigger as shown in FIG. 10 so as to show a fast flow.
Similarly, the data for green color (G) show that the data having a larger value have larger variance in order to display the data having larger variance brighter.
Namely, the display of a color Doppler image is made by a method described in the next place when an RGB display system stipulated by Commission Internationale de Enluminure (CIE) is used.
As described in "Television Information Engineering Handbook" pp. 18-21, edited by The Institute of Television Engineers of Japan, published by Ohm Company, color stimulus [F] of a picture element may be defined by a color equation in equation (1) when looking at a displayed image in picture element unit. Here, it is assumed that [R], [G] and [B] show reference color stimuli and R, G and B show units thereof, and color stimulus [F] of a picture element is produced by mixing them with one another, thus forming a color picture image. EQU [F].ident.R[R]+G[G]+B[B] (1)
Thus, a color Doppler image is displayed by assigning [R] as information showing the direction for expressing a blood flow moving on toward the ultrasonic beam generated by the probe and assigning R unit as information proportioned to the velocity thereof. Further, display is made by assigning [B] as information showing the direction and assigning B unit as information proportioned to the velocity thereof in order to express a blood flow getting away from the ultrasonic beam generated by the probe. Furthermore, display is made by assigning [G] as information showing variance and assigning G unit as information proportioned to the state of the variance in order to show the state of variance when there is velocity variance in respective blood flow described above. Then, a color Doppler image is formed by obtaining color stimuli [F] in picture element unit in accordance with the above-described method and synthesizing them.
As it may be realized from the above description, the data 5 for red color (R) show the distribution of moving velocity having a first moving direction (a direction of moving on toward the ultrasonic beam) of a moving substance such as blood in an object to be examined on a predetermined sliced plane of an object to be examined. Further, the data 7 for blue color (B) show the distribution of moving velocity having a second moving direction (a direction of getting away from the ultrasonic beam) of the moving substance in the object to be examined on the sliced plane. Further, the data 6 for green color (G) show the distribution of moving velocity variance of the moving substance in the object to be examined on the sliced plane.
Further, a method for displaying a color three-dimensional image using the Doppler image data described above has been heretofore proposed. This conventional method will be described with reference to FIG. 9. In FIG. 9, first, a plurality of Doppler image data 8 scanned at appropriate slice intervals with respect to a diagnosis region of an object to be examined are generated. Besides, a flow in a certain blood vessel is adopted as the object. Next, the respective color Doppler image data 8 are separated into data 9 of a red color (R) indicating a flow moving on toward the ultrasonic beam generated by the probe, data 10 of a blue color (B) indicating a flow getting away therefrom, and data 11 of a green color (G) indicating velocity variance of the stream. Next, profile points of the contoured images on respective sliced planes, e.g., points corresponding to positions of blood vessels are extracted after binarization by threshold processing for each of data 9, 10 and 11 in respective colors, and the extracted profile points are arranged on the respective sliced planes so as to reconstruct three-dimensional images 12, 13 and 14 in respective colors of red, blue and green by depth shading algorithm. Thereafter, a three-dimensional color Doppler image 15 has been displayed on a scope by superposing three-dimensional images 12, 13 and 14 in respective colors reconstructed as described above related to the distances from a certain predetermined visual point plane.
In such conventional three-dimensional color Doppler image display, however, the data 9 of a red color (R) and the data 10 of a blue color (B) showing a state of a flow of a blood flow, and the data 11 of a green color (G) showing velocity variance of a blood flow are processed with binarization by threshold processing when the three-dimensional images 12, 13 and 14 in respective colors shown in FIG. 9 are formed. Therefore, information on blood flow velocity and information on velocity variance have disappeared, and only information on directivity of a flow showing whether the flow is coming on toward the ultrasonic beam generated by the probe or the flow is getting away therefrom was obtainable or the information was converted into information only indicating whether there was velocity variance or not. Thus, it has been impossible to display information on the velocity of a blood flow and information on velocity variance which originally belong to a color Doppler image in an ultrasonic diagnosis apparatus having color Doppler instrumentation function with a three-dimensional image, thus being unable to display information effective for diagnosis.